Weather radar systems used aboard commercial and private aircraft are dependant on transmissivity of the radome in front of the weather radar antenna to permit transmission and reception of weather radar signals. However, long exposure to impact by rain, hail, dust, and other objects can cause the protective outer surface of the radome to degrade or possibly delaminate. Specifically, the region at the front of the radome degrades faster then other portions of the outer surface of the radome due to driving rain. When the outer surface of the radome becomes degraded, water may then begin to penetrate the radome. The water is retained by the radome material and can degrade the transmissivity of the radome and, in turn, the sensitivity of the radar. In operation, it is not apparent to the radar operator that water penetration has occurred or that possible degradation of radar performance may have occurred.
As currently known in the art, radomes are routinely removed on the ground for inspection, replacement, or reinstallation. For example, testing of radomes using currently known methods entails removing the radome from the aircraft, placing the radome on a test set, and measuring transmissivity of the radome by measuring the loss from one antenna placed inside the radome and a second test antenna just opposite and outside the radome. Such maintenance work removes the aircraft from service, costing time and money that may be unnecessarily spent. Further, improper repairs made to a radome after substantial damage, such as that from a bird strike, can result in distortion of antenna beams and poor transmissivity. Such problems may not be detected until the next scheduled maintenance.
In addition, conditions that cause poor radome performance in operation, such as wetting of the outer surface due to rain, may not exist on the ground where the radome is tested. In such a case, the radome may be erroneously approved for return to service.
Thus, there is an unmet need in the art for a method of monitoring radome conditions while the radome is in operation, thereby increasing radar reliability and improving cost effectiveness of radar operation and maintenance.
A system and method for automated in-place detection of radome condition is provided. The present invention measures variable reflectivity of a radome directly in front of a typical weather radar antenna by using a radar that operates at a frequency that includes multiple half-wave lengths of the weather radar. As is known, a normal radome with good transmissivity will provide a very low reflection to incident energy at the operating frequency of the weather radar and at a few multiples of the operating frequency of the weather radar. However, presence of water within the radome walls, or a change in dielectric constant of the radome due to poor repairs, will significantly increase absorption and reflection of any incident radio frequency energy. Thus, the invention includes a low power radar operating at a harmonic of the operating frequency of the weather radar. The radar of the invention continuously monitors reflection coefficients of a radome and compares the reflection coefficients to a stored table of data. A reflection coefficient that exceeds the corresponding stored reflection coefficient for that location of the radome by a predetermined factor indicates a possible radome failure.
According to the invention, a system and method for performing automated in-place measurement of reflectivity of a radome of an airplane is provided. The system includes a radar drive circuit that is arranged to generate radar signals at a predetermined frequency. An antenna is arranged to receive the generated radar signals from the radar drive circuit, and is arranged to transmit radar waves at the predetermined frequency. The antenna is arranged to receive radar return waves from the radome. The antenna is mountable on a scanning apparatus that is arranged to scan a substantial area of the radome. A signal processor is arranged to process the radar return waves from the radome that are received by the antenna. The signal processor is arranged to determine whether magnitude of the radar return waves from the radome exceeds a predetermined level for a given position on the radome. When the magnitude of the radar return waves exceeds the predetermined level, an alert signal is generated and provided to an operator.